2G (GSM) and 3G (UMTS/UTRA) mobile telecommunications networks have a radio interface in which user data and signalling may be sent either on a dedicated channel (DCH) allocated to a particular mobile terminal (for a given service offered to the mobile terminal) or on a common channel. Common channels include the random access channel (RACH), forward link access channel (FACH), broadcast channel (BCH) and the paging channel (PCH).
The RACH is used only in the uplink direction. Because the RACH is not reserved, there is a risk that multiple mobile terminals will use it simultaneously so that a “collision” occurs on the radio path and data cannot be successfully received by the network. When using the RACH, an identifier of the mobile terminal originating the transfer is sent.
Burst transmission power on the RACH is determined using open loop power control. Prior to the transmission of a random access burst, the mobile terminal measures the received power on the downlink primary control physical channel (CCPCH). Additionally, the network informs the mobile terminal on the BCH channel about the transmission power of the CCPCH channel. In addition to these data, the transmission power determination uses the uplink interface level information as well as information about the required signal-to-interference ratio (SIR), which are sent to the mobile terminal on the BCH.
A downlink BCH uses a fixed transfer rate. The BCH is used to pass parameters and system information about, and the capabilities of, the current cell in which a mobile terminal is located, and also information about, and the capabilities of, the overall telecommunications system/network.
The BCH parameters and system information may include:
BCH Configuration information—The BCH is split into at least two parts, with the configuration of the second part transmitted in the first part; however the configuration may be common for the whole frequency band.
RACH Configuration information—The system information provides a configuration of the RACH in terms of its location/occurrence in frequency/time/code domains, as well as the maximum transmit power of the UE, and the maximum number of access attempts.
PCH Configuration information—The system information provides a configuration of the PCH in terms of its location/occurrence in frequency/time domains for each paging group. The mobile terminals are split into a number of paging groups.
Measurement Control information—Information is provided by the eNodeB to control the accuracy (frequency/averaging period) which the UE has to meet when measuring the cells of the serving or neighbouring eNodeBs.
Mobility Control information—Information passed to the mobile terminal to control idle mode mobility, including the timer values (e.g. periodic tracking area timer, hysteresis for specific frequency bands, hysteresis for Tracking Area boundaries, hysteresis for cell change, hysteresis for inter RAT change, cell-reselection failure timers).
The quantity and periodicity of the BCH is critical for various reasons, including the following reasons.
Firstly, the BCH has to be successfully received with a high probability over the whole coverage area of the cell. There are no specific retransmissions to individual mobile terminals. Therefore, a mobile terminal that does not successfully receive the BCH is not provided with coverage by the cell.
Secondly, for a mobile terminal in the idle or inactive state, the periodicity of the BCH determines how long the mobile terminal will be out of service after having performed cell reselection. The newly selected cell cannot provide coverage until the full set of system information transmitted in the BCH is received by the mobile terminal.
Thirdly, the quantity and periodicity of the BCH will determine the bandwidth required for the BCH transmission. The higher the quantity of the BCH data and the more frequently that it is transmitted requires increased bandwidth and reduces the efficiency of the radio network (that is, a higher proportion of the available bandwidth is used for BCH transmissions, rather than other transmissions).
In known telecommunications systems information transmitted in the BCH includes nearly all the information that enables the mobile terminal to access the relevant cell and provide knowledge of the radio features supported by the cell. To transmit this information, a significant quantity of data must be transmitted at regular intervals on the BCH, consuming radio resources that could otherwise be used for other purposes. Much of the system information for different cells of a particular PLMN is likely to be similar, with a small number of parameter combinations varying from cell to cell.
Also, in known telecommunications systems, due to the nature of the BCH, the same system data are received by all terminals in the same cell. Further, when a mobile terminal is in the active state, in connected mode, and “handover” occurs as the terminal moves from one cell to another, the system information may be received in the Handover Signalling, so the system information transmitted in BCH of the new cell is redundant.
Accordingly, it would be desirable to provide an improved arrangement where the quantity of data transmitted in the BCH is reduced and to provide an arrangement that allows the system information to be different for each mobile terminal in a cell.
A development of 3G mobile telecommunications is “evolved” UTRA or E-UTRA, also referred to as SAE (System Architecture Evolution)/LTE (Long Term Evolution). LTE telecommunications will also use a BCH of a similar type to that used in 3G. The system described herein is applicable to many types of radio access networks (RANs) including 2G, 3G and LTE.